The present invention relates to control apparatus for programmable manipulators (industrial robots) of the type that perform predetermined work cycles with respect to movable workpieces.
Industrial robots or manipulators are generally used for increasing the efficienty of personnel and for saving manpower in existing facilities. In numerous situations the manipulator is required to perform a predetermined work cycle with respect to workpieces on a continuously moving conveyor.
In one arrangement of the prior art, a manipulator is mounted on a truck to be carried by the truck in synchronism with the movement of the workpiece to perform a work cycle in accordance with the program stored in the memory of the manipulator control apparatus. Thus, there is no change in the relative positions between the manipulator and the workpiece. In this arrangement, however, the truck is by necessity a bulky and rather massive mechanism. Further, complicated control apparatus is required to accomplish the precise movement of the manipulator and truck arrangement to follow the workpiece. Further, it is quite difficult to rapidly return the truck to the original position. In addition, the system requires a large space along the workpiece path.
In another apparatus of the prior art, the manipulator is fixedly positioned and has a working arm adapted to follow moving workpieces. When it is desired to move along a continuous trace on a workpiece, the moving position of the workpiece on the conveyor is preliminary memorized or taught together with the coordinate positions of each axis of the robot on the work cycle path or trace. In a replay or work cycle, the position of the workpiece is detected and corresponding stored coordinate values are sequentially read out for each axis of the robot. In this system, it is possible to perform a work cycle continuously on a moving workpiece and the working arm can be rapidly returned simply by storing the initial point as a command signal for the manipulator. However, since the positions of the workpiece and the positions of the manipulator arm are associated in a fixed relationship, it is difficult to continue a desired work cycle and to move along the predetermined path or trace at a predetermined working arm speed relative to the workpiece when there has been an abrupt change in the workpiece speed or when the workpiece has stopped. Thus, under such circumstances, it is extremely difficult to perform an arc-welding or painting operation.
Other prior art arrangements have been proposed to solve this problem by storing the coordinates of the manipulator arm with respect to the workpiece for the predetermined work cycle path, detecting the varying position of the workpiece during the replay of the work cycle, and transforming the stored coordinates of the manipulator through calculations in accordance with the detected workpiece position. However, such calculations are complicated, time consuming and require the use of a high speed computer. Therefore, the design is considered as relatively impractical.
Accordingly, it is a principal object of the present invention to provide control apparatus for a programmable manipulator or robot that avoids one or more of the disadvantages of the aforementioned prior art arrangements.
It is another object of the present invention to provide control apparatus for a robot or programmable manipulator wherein the manipulator performs a predetermined work cycle with respect to a moving workpiece in a continuous manner and at a predetermined speed with respect to the workpiece in spite of variable workpiece movement or stopping of the workpiece.
It is a further object of the present invention to provide a programmable manipulator for performing a predetermined work cycle with respect to a workpiece moving at a variable speed wherein positional data is stored during a teach phase representing a predetermined work cycle with respect to the workpiece for at least two respective workpiece locations, and the stored data utilized in replay to perform the predetermined work cycle with respect to the workpiece.
It is yet another object of the present invention to provide manipulator control apparatus for a programmed manipulator having a manipulator arm, the control apparatus generating interpolation command signals from stored data wherein the interpolation command signals account for the position and movement of a workpiece and are utilized to control movement of the manipulator apparatus to perform a predetermined work cycle with respect to the workpiece; the stored data is recorded during a teach phase and represents the manipulator arm positions to define the predetermined work cycle with respect to the workpiece at two or more locations of the workpiece along a predetermined workpiece path.
Briefly, in accordance with the present invention, there is provided control apparatus to control a programmable manipulator arm movable in a plurality of axes to perform a predetermined pattern of work operations in a replay cycle with respect to a movable workpiece while the workpiece is moving or is stationary at a point along a predetermined workpiece path. In replay, the control apparatus generates interpolation control signals from stored data in accordance with the workpiece position. The stored data includes two or more series of signals representing manipulator arm positions to accomplish the predetermined pattern of work operations with respect to the workpiece at two or more respective positions of the workpiece.
During replay, data is read out from the two series of signals that are associated with workpiece positions on either side of the present workpiece position. In one arrangement, one signal is read out from each of the two series corresponding to the same sequential element in each series and representing the same point in the predetermined work operation pattern with respect to the workpiece. The sequential elements in the series are successively read out to perform the predetermined pattern of work operations with respect to the workpiece.
The control apparatus performs a linear interpolation operation between the signals from the two series and the present position of the workpiece.
The control apparatus in one embodiment includes a linear interpolation unit having a stage for developing a signal equal to the difference between the two signals, an arithmetic stage for multiplying the difference signal by l/d where l represents the present workpiece position between the workpiece positions associated with the two series and d represents the distance between the respective workpiece positions associated with the two series, and a stage for combining the signal from the first series and the signal developed by the arithmetic stage.
The invention both as to its organization and method of operation thereof with further objects and advantages thereof will best be understood by reference to the following specification taken in connection with the accompanying drawings.